1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same. In particular, the present invention relates to a semiconductor device that uses a metal film as a gate electrode and a resistive element, and a method of manufacturing the same.
2. Description of Related Art
In a semiconductor device, a gate electrode is formed on a substrate. To use a metal electrode as the gate electrode is considered in order to prevent carrier depletion of the gate electrode at the gate/dielectric interface and to reduce resistance of the gate electrode. Also, a resistive element as well as the gate electrode is sometimes formed on the substrate. Material of the resistive element may be polysilicon.
If polysilicon is used fox both of the gate electrode and the resistive element, the gate electrode and the resistive element can be formed at the same time. However, in a case where a metal electrode is used as the gate electrode while polysilicon is used for the resistive element, the gate electrode and the resistive element cannot be formed by the same process, which complicates fabrication processes.
Japanese Laid-Open Patent Application JP-2001-351877 discloses a related technique, FIG. 1 is a cross-sectional view of a semiconductor device according to the related technique. As shown in FIG. 1, a gate electrode and a resistive element are formed on a substrate. The gate electrode consists of a lower layer gate electrode and an upper layer gate electrode. The resistive element and the lower layer gate electrode are formed of the same material, which suppresses increase in the number of fabrication processes.
Japanese Laid-Open Patent Application JP-2000-307060 discloses another related technique. According to the related technique, a polysilicon film that is a material film of a resistive element is covered by refractory metal silicide, and then the refractory metal silicide is left unremoved only on a connection point of the resistive element. As a result, excessive etching can be suppressed when forming a contact.
The inventor of the present application has recognized the following points. Let us consider a case where a metal electrode is used as a gate electrode. In this case, it may be considered to use the same metal film not only for the gate electrode but also for a resistive element in order to simplify the fabrication processes. However, the metal film has higher conductivity as compared with a polysilicon film. Thus, a film thickness of the resistive element has to be made smaller as compared with a case when a polysilicon film is used, in order to achieve a desired resistance value by the resistive element.
Note here that an upper layer wiring is connected to the resistive element through a contact hole. It is necessary for forming the contact hole to etch a film covering the resistive element. However, when the film thickness of the resistive element is small, the resistive element is also removed by the etching for forming the contact hole.